1. Field of the Invention
The present invention pertains to the art of fluid driven actuator systems and, more particularly, to a fluidic stiffness enhancing system for use with fluid driven actuators.
2. Discussion of the Prior Art
Fluid driven actuators are widely known in the art. In many environments in which actuators are used, an important property of the actuator is its stiffness. In general, a fluid driven actuator includes at least one cylinder that is divided into two variable volume chambers by a piston. Such actuators can be configured as linear or rotary, as is well known in the field of fluid actuators. Fluid pressure can be selectively supplied to either of the two chambers fluidly through a servo-valve or the like to drive the piston, which actually repositions a motion output piston rod or shaft to which the piston is secured. The actuator normally possesses a "stiffness" that can be described in terms of the resistance of the piston to motion in response to an exterior force applied directly to the piston rod. However, if a system failure occurs that results in a pressure loss in one of the chambers, the chamber cannot contribute to the stiffness (i.e., resistance to piston rod movement) of the actuator. It is highly desirable in many applications, particularly in aerospace or aircraft environments, to maintain high stiffness in an actuator that may suddenly lose system pressure.
It would be desirable in the event of such a failure for the chamber to still contribute to the stiffness of the actuator. Ideally, the chamber would provide little resistance to motion at low, control frequencies, yet provide a high degree of resistance to high frequency forces, such as flutter forces developed on a control surface of an aircraft in flight.
Therefore, there exists a need in the art for a system for use in enhancing the stiffness of a fluid driven actuator in the event of a failure in the ability of at least one of the chambers of the actuator to contribute to the stiffness of the actuator.